The invention pertains to an adjusting device for locking and unlocking motor vehicle doors.
Electric motors are increasingly used as adjusting units for central door locking system on motor vehicles. There are systems in which the direction of rotation at the electric motor is not variable and the actuator is driven by the electric motor via a crank mechanism. In these systems a limit switch is associated with each adjusting unit to ensure that the actuator is always stopped in the end positions. Furthermore each adjusting unit includes a bilaterally effective coupling which provides for compensation between the required adjusting stroke of the actuator and the adjusting path permitted by the mounting conditions in a motor vehicle door. The system would not be operable, if this adjusting stroke predetermined by the crank mechanism were greater than the maximally adjusting path of the lock latch driven by the actuator.
Systems of this kind have been described in the German specifications OS Nos. 2 946 889 and 3 022 290 and in the U.S. Pat. No. 2,765,647. These systems have the advantage that the electric motors can be grounded and therefore the amount of circuitry is small. On the other hand an increased amount of circuitry is necessary because a limit switch and a coupling are assigned to each adjusting unit.
There are also central door locking systems for motor vehicles in which the direction of rotation of the electric motor is reversible. In these systems limit switches are not needed for each adjusting unit, because the end positions of the actuator can be preset by a mechanical stop and the actuator can be returned to its original position from any position by a change of the direction of rotation of the electric motor. The electric motors of systems of this kind are designed for short-time operation and therefore are automatically switched off after carrying out an adjustment. For this purpose a timing element is switched on via the operating switch which controls all electric motors in parallel. U.S. Pat. No. 3,653,237 describes a system of this kind including an electronic timing element. German specification OS No. 3 049 120 indicates that the operating switch itself can be formed as a mechanically operating pulse switch. Finally a system is described in German specification OS No. 3 248 194, in which a separate servo motor is used as a timing element to switch off the adjusting units connected in parallel after it has run through a given angle of rotation. All these embodiments require an additional element, namely a timing element, in addition to the adjusting unit thus increasing the production costs and the space requirement.
It should be noted that the structure of German specification OS No. 3 248 194, has the further disadvantage that the additional servo motor used as a timing element has a different switching characteristic from the electric motors of the adjusting units.